1. Field of the Invention
The present invention relates to a thermal flow meter, a thermal flow meter control method, and a sensor element of a thermal flow meter. More particularly, the present invention relates to a thermal flow meter that is suitable for detecting the flow rate of the intake air or exhaust gas of an engine, a method of controlling the thermal flow meter, and a sensor element of the thermal flow meter.
2. Background Art
Conventionally, as this kind of thermal flow meter, at least two resistors are arranged in a fluid, as illustrated in FIG. 28. One of the resistors is used as a resistance temperature detector that detects the temperature of the fluid, and the other is used as a heating resistor that detects a flow rate. By always maintaining the respective temperature differences (ΔTh) constant, measurement of the mass flow rate of the fluid can be carried out.
Further, as a conventional thermal flow meter, a fluid flow rate measuring device has been proposed that measures a flow rate of a fluid, particularly an airflow rate that is necessary for combustion in an internal-combustion engine, using at least two temperature-dependent resistors that are disposed in the fluid, which is provided with two resistance measuring circuits, in particular, bridge circuits, that are each connected to a temperature-dependent resistor. In this fluid flow rate measuring device, the temperature-dependent resistors that are connected to each bridge circuit are caused to generate heat of respectively different predetermined temperatures (for example, see Patent Document 1).    [Patent Document 1] JP Patent Publication (Kokai) No. 59-136620A (1984)